For practical and decorative reasons it is usually frequent that a building block, such as a wall-, floor- or ceiling-surface is illuminated by one or several separate sources of light, e.g. so called spotlights, directed to the surface in question. Nowadays it is also popular to mount lamps in building elements, such that they are recessed and/or flush with the surface, which provide some lighting over the surface and some lighting in adjoining rooms adjacent to the surface.
From GB 1561142 it is previously known to arrange light guiding bars comprising bundles of optical fibres, in drilled through holes between two opposite sides of a building element. Light from a light source that illuminates a rear side of the element is guided through the bars bundles of fibres to the opposite side.
However, it is impractical, time consuming and costly, as mentioned above, to mount light sources or optical cables in prepared building elements or in built walls, ceilings or floors, in order to transfer light through the building element, especially if small light sources, at certain points, shall be mounted in the building element. If a considerable part of a surface shall emit light, it is easily appreciated that the work will be lengthy since a large number of holes have to be made. Besides, only mounting of a limited number of light sources in the building element can be done by these known methods, if not influencing the length of the element. In case a light emitting and/or illuminating effect is desired to be provided over a considerable part of a surface, when a separate light source cannot or is not desired to be used, it is in practice only possible by mounting relatively light-spreading sources in the surface layer of the building element in order to avoid influencing its strength. Thus, formation of the extent of illumination and the decorative effect becomes restricted.